This invention relates generally to plasma processing in the fabrication of semiconductor devices and, more particularly, to techniques for removing particulate matter from semiconductor substrates in plasma processing chambers, such as plasma enhanced chemical vapor deposition (PECVD), reactive ion etch (RIE) or sputter etch processing chambers. As is well known, semiconductor device geometries have been steadily shrinking in scale, and key features of devices have become more densely packed in each integrated circuit. When dealing with structural features at a microscopic level, engineers throughout the integrated circuit industry have had to deal with a critical problem of particulate control. Simply stated, the presence of particulates on integrated circuit substrates causes defects in some of the circuits. In most integrated circuit fabrication, many identical integrated circuits are formed on a single wafer, using a step-and-repeat lithographical process. The percentage of properly functioning integrated circuits formed on a wafer is referred to as the yield. Higher concentrations of particulates result in lower production yields. The problem is further compounded in the fabrication of extremely large, "wafer scale" integrated circuits, where significant particulate contamination can render an entire wafer useless.
It is generally agreed that the major source of particulates is the processing equipment itself, but there are no commercially available methods for removing particulates from wafers after their entry into a processing chamber. Because the present invention uses electrostatic forces to remove particulates from a processing chamber, it should be noted that the use of electrostatic energy to exert forces on particles has been known for many years, and was first demonstrated by Miliken in historic work discovering and quantifying the charge of the electron. Miliken's particles were small oil droplets, which he demonstrated could be moved up or down by the application of electrostatic fields.
A well known phenomenon in plasma etch reactors is the generation of a direct current (dc) bias between the plasma and a lower electrode to which rf power is applied. The dc bias accelerates positive ions in the reactor chamber toward the lower electrode, to which a semiconductor wafer is secured for etching. The energy of the ions accelerated from the plasma is one of the most important factors that determine the rate at which etching of the wafer takes place. As a result of the dc bias phenomenon, plasma etch processors already have a built-in technique for launching particulates electrostatically from the wafer surface. However, when there is no dc bias, as in PECVD processes, any particulates on the wafer surface are not automatically removed. Simply applying a permanent dc bias to the wafer does not work because the plasma tends to react in a way that compensates for the bias. Mobile charges in the plasma move to a position that shields out the effect of the biased surface.
It will be appreciated that there is an increasing need for particulate removal in semiconductor plasma processing chambers, such as PECVD chambers. The present invention fulfills this need.